1. Field of the Invention
The present invention relates to a navigation apparatus, and more particularly to a method for calculating an optimum travel route using a navigation apparatus.
2. Description of the Related Art
Navigation apparatuses using a GPS (Global Positioning System) have been recently installed in movable bodies, i.e., various vehicles such as vessels, airplanes, cars, etc. The navigation apparatus receives radio waves representing latitude, longitude, altitude, etc. from a plurality of satellites of the GPS, thus calculating the present location of a movable body. The navigation apparatus displays map information including the present location of the movable body according to stored map data. That is, the conventional navigation apparatus provides to drivers various necessary information displayed via a screen, such as a present traveling speed of the movable body, a travel route designated by a driver prior to traveling, and an optimum travel route to his/her desired destination, using the information received from the GPS.
FIG. 1 is a functional block diagram of a conventional navigation apparatus 100. With reference to FIG. 1, a present location detecting unit 110 includes a present location calculating unit 111, a GPS receiver 113, and a sensing unit 115. The present location detecting unit 110 detects the present location of a movable body. The GPS receiver 113 receives radio waves transmitted from a plurality of satellites of the GPS via an antenna, thereby calculating a virtual coordinate of the present location of the movable body. The sensing unit 115 includes a gyro sensor and a speed sensor. The sensing unit 115 senses the turning angle and speed of a vehicle via the gyro and speed sensors. The present location calculating unit 111 calculates a present virtual location of the vehicle based on the turning angle and speed of the vehicle, transmitted from the sensing unit, 115. Then, the present location calculating unit 111 selects either the virtual coordinate of the present location of the vehicle transmitted from the GPS receiver 113, or the calculated virtual location of the vehicle. Here, the present location calculating unit 111 calculates not only the present location of the vehicle but also the traveling information such as the traveling speed and direction of the vehicle. The calculated traveling information of the vehicle is transmitted to a navigation controller 120. A map information memory 130 stores the map information and additional information. A manipulating unit 160 includes a plurality of keys, and supplies a key order inputted by a driver to the navigation controller so as to operate the navigation apparatus 100. A displaying unit 150 displays the map information read by the map information memory 130 and status of the navigation apparatus 100 while performing various functions. Based on the traveling information obtained by the present location calculating unit 111, the navigation controller 120 reads map data of surrounding areas from the map information memory 130, and then displays the read data on the displaying unit 150. A vehicle signal interfacing unit 140 transmits state information of the vehicle to a navigation controller 18, where state information may be, for example, whether an air-bag set is available in the vehicle, whether the engine is functioning properly, or how much fuel remains in the fuel tank.
When a driver designates a desired destination and requests travel route information to the destination, the navigation controller 120 calculates an optimum travel route from the present location of the driver's vehicle or a departure point designated by the driver to the destination, i.e., the shortest travel route, and then displays the calculated result of the optimum travel route on a screen. For example, the calculated optimum travel route is displayed on a map on the screen.
During travel, the conventional navigation apparatus installed in the vehicle considers the present location of the vehicle as the departure point when the driver requests the optimum travel route information. Then, the conventional navigation apparatus calculates the optimum travel route from the departure point to the destination, and displays the calculated result. When the conventional navigation apparatus calculates the optimum travel route, location information of the vehicle that changes during the calculation time is not considered. Therefore, at a point of time when the conventional navigation apparatus provides the calculated result of the optimum travel route, the vehicle that has requested the optimum travel route has moved to a location different from the original departure point. As a result, the vehicle, which has requested the optimum travel route, may be located outside of the calculated optimum travel route.
In order to solve such a problem, the conventional navigation apparatus determines a virtual location of the vehicle predicted after the time taken to calculate the optimum travel route based on the traveling speed and direction information of the vehicle which has requested the optimum travel route. Then, the conventional navigation apparatus considers the above-determined virtual location as a departure point, thus calculating the optimum travel route from the virtual location to the destination. In this case, the conventional navigation apparatus does not consider characteristics of roads but considers only the traveling speed and direction of the vehicle, and considers the virtual location past a certain distance from the present location of the vehicle as the departure point. Therefore, the departure point may be actually unusable.
As described above, using the conventional navigation apparatus, the vehicle which has requested the optimum travel route may be located outside of the optimum travel route obtained by the navigation apparatus installed in the vehicle.
When the vehicle moves to a next link of the map, in cases where it makes a right or left turn, the actual travel time of the vehicle becomes longer than the mean travel time stored in the map data. However, the conventional navigation apparatus does not consider this point, but uses only the travel time information calculated by the travel distance in detecting the optimum travel route. Therefore, although the travel time via the optimum travel route calculated by the conventional navigation apparatus is detected to be comparatively short, the actual travel time of the vehicle may be longer than the calculated travel time.